Flexible circuit configurations are advantageous for use, inter alia, in applications in which the circuit configuration must have permanent flexible properties, in particular in body implants or objects which are at least limitedly flexible in use, such as credit cards.
A structure of a credit card having an integrated electromagnetic configuration is known from US 2007/0241201 A1. The card consists of multiple layers, which are fixedly connected to one another, a middle layer forming a flexible circuit board, on which a flexible circuit configuration having a plurality of coils in a multilayer layer sequence is in turn situated.
Such a flexible circuit configuration having coils, which enclose a core made of magnetic material, can be produced, for example, in that a layer sequence of insulating layers, conducting layers, and at least one layer made of magnetic material is deposited on a rigid silicon substrate, and at least multiple layers are each structured differently after being deposited. The structuring is typically performed by photolithography using different masks.
For a high packing density of passive and/or active circuit elements in the flexible circuit configuration, such as a high number of coils each having multiple turns on only a short overall length of the magnetic chip in the above-mentioned credit card application, in addition to a fine resolution of the structures, a high precision during the continuously new orientation of the masks relative to structures which have already been created is required in particular. This is achievable per se using a rigid substrate, such as a silicon wafer, on which the layer sequence for a plurality of flexible circuit configurations is preferably deposited and which maintains a fixed position during the typical multiple temperature changes. The flexible circuit configuration is removed from the substrate after the creation of the layer sequence, e.g., by dissolving an adhesive layer between substrate and layer sequence or by mechanical peeling off of the substrate surface. Damage to the flexible circuit substrate, which is only fractions of a millimeter thick, can in turn result due to mechanical strains and/or due to the action of etching media, solvents, or the like.